Meet Circinus X-1: It’s all that remains of a star that exploded approximately 2,500 years ago (basically last week, on a cosmic scale). Within the system is a neutron star (the remnant of the now-dead star) and a companion, interactions between the two generate x-rays, and a rather impressive nebula has taken shape around them.
These things are not unusual. What was unusual, however, happened in 2013, when Circinus X-1 suddenly became one of the brightest x-ray sources in the sky. And then, just like that, the light gave way to darkness once more, but not before astronomers got a decent look at it.
Followup observations revealed a series of rings around Circinus X-1, which can be likened to ripples propagating through a huge pond, only with color. This is called a light echo.